export let vertexShaderSource = `
      attribute vec2 a_position;
      // 世界矩阵
      uniform mat3 u_world;
      // 单位矩阵
      uniform mat3 u_unit;
      
      void main (){
        vec3 p = u_world * u_unit * vec3(a_position, 1);
        gl_Position = vec4(p.xy, 0, 1);
      }
`
